This invention relates in general to brake systems for motor vehicles, and in particular to a method of controlling electrohydraulic boosters for vehicle brake systems.
Conventional vehicle brake systems are constructed such that the braking force developed by the system is generally proportional to the force applied by the vehicle operator on a vehicle brake pedal. The pedal is linked to a piston in a master cylinder that moves to pressurize the fluid of the brake system, and thus actuate the individual wheel brakes. Generally, in order to provide a sufficiently high pressure to operate the wheel brakes without requiring an excessive effort by the operator, most vehicles include a "boosted" power brake system wherein the force applied to the brake pedal by the operator is amplified or boosted before being applied to the master cylinder. In automobiles and light trucks, this is typically accomplished by incorporating either a vacuum or hydraulically operated boost piston assembly between the brake pedal and the master cylinder.
Vacuum operated boost piston assemblies utilize the pressure differences between the atmosphere and the vehicle's engine vacuum to develop a force across a boost piston or diaphragm. The force developed by this differential pressure across the boost piston may be many times that that could be developed by the operator by pressing against the pedal, and is applied to the piston of the master cylinder to actuate the brakes.
In brake systems with electrohydraulic brake boosters, hydraulic boost piston assemblies utilize the pressure developed by a hydraulic system, such as the vehicle's power steering system, to apply a force to a boost piston that is connected to operate a master cylinder of the brake system. Hydraulic boost piston assemblies of this type, and the associated brake boost pressure control systems, are described, for example, in International Patent Application Nos. PCT/US97/08151 and PCT/TJS97/07640, the disclosures of that are hereby incorporated by reference. The force applied to the piston of the brake system master cylinder via the boost piston of the hydraulic boost system, may be many times that that could be applied by the operator of the vehicle without a boost system. Electronic controls are provided that regulate the application of force by the boost piston according to pre-programmed instructions. Because of this electronic control of the hydraulic brake boosters, these brake boosters can easily be integrated into systems where the electronic control of the brake boost is used for traction control (TC), anti-lock braking (ABS), vehicle stability control (VSC), hill hold, theft protection, collision avoidance, panic brake assist, brake induced vehicular deceleration control, brake pedal travel control, and brake "pedal feel" characteristic tailoring. "Pedal feel" refers to the relationship between the force a driver applies to a brake pedal during vehicle braking and the resultant movement of the brake pedal.